Metal-oxide-semiconductor field effect transistors (MOSFETs) are semiconductor devices commonly employed for switching power on and off. A MOSFET includes a source region, a drain region, and a body extending between the source and drain regions. The body is separated from a gate electrode by a thin dielectric layer, so that a voltage applied to the gate electrode can control whether a conductive channel forms between the source and the drain regions. When the gate voltage is applied and the conductive channel is formed, the MOSFET enables current to pass through the device (between the drain and source regions), subject to an on-state resistance. When the conductive channel is absent, the device blocks current flow unless a drain breakdown voltage is reached.
It is desirable to make on-state resistance as small as possible while making the drain breakdown voltage as high as possible, but traditionally these parameters have had to be traded-off against each other. This trade-off constraint has been relaxed (though not eliminated) through the use of so-called Laterally Diffused MOSFET (LDMOS) devices. Such devices employ light doping on the drain side to provide in a wide depletion layer with high blocking voltage. But the depletion layer also extends laterally from the devices, which must then be spaced further apart to preserve the breakdown voltage. This spacing requirement limits the utility of such devices in tight-pitch environments such as embedded memory.